Concrete is usually provided with reinforcement in order to increase its load-bearing capacity. This reinforcement typically involves concrete rod steels or mat reinforcement (reinforcement rods provided in a grid pattern), around which the concrete mass is poured during construction.
In this connection, it is known that a thin oxide layer forms on the metal reinforcements in the highly alkaline environment produced by the concrete, the layer protecting against further corrosion. However, it is known as a problem that the protective oxide layer can be destroyed by external influences, for example as the result of chlorides that penetrate the concrete all the way to the reinforcement, or also as the result of carbonization of the concrete, thereby making it possible for defects in the passive oxide layer to form, and therefore defects that form locally can corrode further, particularly under the influence of oxygen and moisture that are normally present in the concrete.
Accordingly, a ferroconcrete structure can lose its load-bearing capacity as the result of advancing corrosion of the reinforcements, and can become a safety risk. It is therefore known in the state of the art to find such corrosion sites by measurement technology measures, for example by the principle of half-cell potential measurement.
This principle takes advantage of the fact that a corrosion site, which can be referred to as base, forms an electrogalvanic cell together with the precious, corrosion-protecting regions of a reinforcement rod, which means that the formation of a potential funnel occurs in the surroundings of the corrosion site, and also that minimal current flows arise.
The method known in the prior art makes use of this, namely in that an electrode referred to as a half cell is contacted with the surface of the concrete, with another contact with a metal reinforcement (armoring) to be investigated being produced by way of a voltmeter, to which end it is necessary to break the concrete up locally in order to obtain access to the reinforcement to be investigated. There is then the possibility of measuring the potentials that have occurred at the local corrosion site that extend all the way to the surface of the concrete, relative to a reference potential, with direct contacting of the metal reinforcement, and of drawing conclusions concerning the position of a corrosion site from the value of the measured potential.
In this connection, it is felt to be disadvantageous, on the one hand, that a measured potential in and of itself does not make sufficient information available so that a conclusion can be drawn concerning the location of a corrosion site, and, on the other hand, it is considered to be particularly disadvantageous that access through the concrete all the way to a metal reinforcement must be created mechanically, by destructive measures, in order to obtain a reference potential. Creation of such access is cost-intensive, time-consuming, and furthermore requires renewed closing of the access point that has been created, after the measurement has been made. Another disadvantage is considered to be the cable connection with the reinforcement connector, where usually very great cable lengths are required.